1================================== 2Kernel Lock Torture Test Operation 3================================== 4 5CONFIG_LOCK_TORTURE_TEST 6======================== 7 8The CONFIG_LOCK_TORTURE_TEST config option provides a kernel module 9that runs torture tests on core kernel locking primitives. The kernel 10module, 'locktorture', may be built after the fact on the running 11kernel to be tested, if desired. The tests periodically output status 12messages via printk(), which can be examined via the dmesg (perhaps 13grepping for "torture"). The test is started when the module is loaded, 14and stops when the module is unloaded. This program is based on how RCU 15is tortured, via rcutorture. 16 17This torture test consists of creating a number of kernel threads which 18acquire the lock and hold it for specific amount of time, thus simulating 19different critical region behaviors. The amount of contention on the lock 20can be simulated by either enlarging this critical region hold time and/or 21creating more kthreads. 22 23 24Module Parameters 25================= 26 27This module has the following parameters: 28 29 30Locktorture-specific 31-------------------- 32 33nwriters_stress 34 Number of kernel threads that will stress exclusive lock 35 ownership (writers). The default value is twice the number 36 of online CPUs. 37 38nreaders_stress 39 Number of kernel threads that will stress shared lock 40 ownership (readers). The default is the same amount of writer 41 locks. If the user did not specify nwriters_stress, then 42 both readers and writers be the amount of online CPUs. 43 44torture_type 45 Type of lock to torture. By default, only spinlocks will 46 be tortured. This module can torture the following locks, 47 with string values as follows: 48 49 - "lock_busted": 50 Simulates a buggy lock implementation. 51 52 - "spin_lock": 53 spin_lock() and spin_unlock() pairs. 54 55 - "spin_lock_irq": 56 spin_lock_irq() and spin_unlock_irq() pairs. 57 58 - "rw_lock": 59 read/write lock() and unlock() rwlock pairs. 60 61 - "rw_lock_irq": 62 read/write lock_irq() and unlock_irq() 63 rwlock pairs. 64 65 - "mutex_lock": 66 mutex_lock() and mutex_unlock() pairs. 67 68 - "rtmutex_lock": 69 rtmutex_lock() and rtmutex_unlock() pairs. 70 Kernel must have CONFIG_RT_MUTEXES=y. 71 72 - "rwsem_lock": 73 read/write down() and up() semaphore pairs. 74 75 76Torture-framework (RCU + locking) 77--------------------------------- 78 79shutdown_secs 80 The number of seconds to run the test before terminating 81 the test and powering off the system. The default is 82 zero, which disables test termination and system shutdown. 83 This capability is useful for automated testing. 84 85onoff_interval 86 The number of seconds between each attempt to execute a 87 randomly selected CPU-hotplug operation. Defaults 88 to zero, which disables CPU hotplugging. In 89 CONFIG_HOTPLUG_CPU=n kernels, locktorture will silently 90 refuse to do any CPU-hotplug operations regardless of 91 what value is specified for onoff_interval. 92 93onoff_holdoff 94 The number of seconds to wait until starting CPU-hotplug 95 operations. This would normally only be used when 96 locktorture was built into the kernel and started 97 automatically at boot time, in which case it is useful 98 in order to avoid confusing boot-time code with CPUs 99 coming and going. This parameter is only useful if 100 CONFIG_HOTPLUG_CPU is enabled. 101 102stat_interval 103 Number of seconds between statistics-related printk()s. 104 By default, locktorture will report stats every 60 seconds. 105 Setting the interval to zero causes the statistics to 106 be printed -only- when the module is unloaded. 107 108stutter 109 The length of time to run the test before pausing for this 110 same period of time. Defaults to "stutter=5", so as 111 to run and pause for (roughly) five-second intervals. 112 Specifying "stutter=0" causes the test to run continuously 113 without pausing. 114 115shuffle_interval 116 The number of seconds to keep the test threads affinitized 117 to a particular subset of the CPUs, defaults to 3 seconds. 118 Used in conjunction with test_no_idle_hz. 119 120verbose 121 Enable verbose debugging printing, via printk(). Enabled 122 by default. This extra information is mostly related to 123 high-level errors and reports from the main 'torture' 124 framework. 125 126 127Statistics 128========== 129 130Statistics are printed in the following format:: 131 132 spin_lock-torture: Writes: Total: 93746064 Max/Min: 0/0 Fail: 0 133 (A) (B) (C) (D) (E) 134 135 (A): Lock type that is being tortured -- torture_type parameter. 136 137 (B): Number of writer lock acquisitions. If dealing with a read/write 138 primitive a second "Reads" statistics line is printed. 139 140 (C): Number of times the lock was acquired. 141 142 (D): Min and max number of times threads failed to acquire the lock. 143 144 (E): true/false values if there were errors acquiring the lock. This should 145 -only- be positive if there is a bug in the locking primitive's 146 implementation. Otherwise a lock should never fail (i.e., spin_lock()). 147 Of course, the same applies for (C), above. A dummy example of this is 148 the "lock_busted" type. 149 150Usage 151===== 152 153The following script may be used to torture locks:: 154 155 #!/bin/sh 156 157 modprobe locktorture 158 sleep 3600 159 rmmod locktorture 160 dmesg | grep torture: 161 162The output can be manually inspected for the error flag of "!!!". 163One could of course create a more elaborate script that automatically 164checked for such errors. The "rmmod" command forces a "SUCCESS", 165"FAILURE", or "RCU_HOTPLUG" indication to be printk()ed. The first 166two are self-explanatory, while the last indicates that while there 167were no locking failures, CPU-hotplug problems were detected. 168 169Also see: Documentation/RCU/torture.rst 170